xTwitter

xTwitter is probably the most complete twitter API written in PHP, it can be used to retrieve information, update satuses and the account of a Twitter user. This free PHP script will send HTTP requests to the Twitter API Web server on behalf of a given user and performs several types of operations.

Currently, this script getting the user statuses aggregated in several ways, updating or deleting statuses, getting, sending and deleting direct messages, adding, deleting and verifying friends and much more.